LOW-MOLECULAR-WEIGHT NITROGENOUS COMPONENTS AND THEIR INFLUENCE ON THE STABILITY OF BEER FOAM

Addition of low molecular weight nitrogenous components, nucleoside (adenosine), nucleotide (AMP), amino acids (glutamic acid, glycine, proline and asparagine) and a tripeptide (glycylglycylglycine) had no effect on the head retention value of beer. Under such conditions of artificial manipulation of the content of low molecular weight beer nitrogenous components no correlation between the nitrogen molecular weight ratio of beer and beer head retention value was observed. Collapsed beer foam was collected and separated into soluble and precipitated fractions. Analysis of collapsed beer foam demonstrated that high molecular weight polypeptide material and isomerised alpha-acids are concentrated in beer foam and are constituents of beer foam precipitate material. Beer foam precipitate material may be stabilised by ionic interactions between polypeptide material and isomerised alpha-acids. Further analysis of beer and collapsed beer foam demonstrated that purine nucleosides are not concentrated in beer foam. Similarly, under conditions simulating beer dispense, amino acids are not concentrated in beer foam. Under strongly selective foaming conditions, such as those encountered in a foam tower, the hydrophobic amino acids, valine, isoleucine, leucine and phenylalanine are concentrated in beer foam.